There has been conventionally known a probe that measures an electromagnetic field by using laser light, an optical fiber, and an EO (electrooptic) material/MO (magnetooptic) material, and evaluation results of microwave circuits and antennas obtained by using the probe have been reported (refer to, e.g., NPL 1). The probe includes an optical fiber and an EO/MO material formed at the leading end of the optical fiber. The probe of such a type can perform high spatial resolution measurement on a circuit board or can perform measurement for a minute or narrow area owing to the minuteness of the EO/MO material serving as a sensor element and narrowness of the optical fiber. In general, only one optical fiber probe is used for measurement, and the probe is fixed to a measurement point or made to scan over an object to be measured.
Further, in recent years, there is reported development of a method (electric field camera) in which a tabular EO material having a size of 1 cm to 2 cm square is placed on an object to be measured and is irradiated with laser light having a beam diameter nearly equal to the plane size of the EO material to measure the electric field distribution of the irradiated area instantaneously (refer to, e.g., NPL 2). The probe of such a type can perform measurement of the electric field distribution at extremely short times without making the probe perform scanning.
In the field of optical communication, a wavelength division multiplex (WDM) communication represents a major breakthrough as a method enabling large capacity and high-speed communication. In this method, by utilizing a fact that light of different ranges of wavelengths can be transmitted by the use of an optical fiber, it is possible to transmit optical signals of a plurality of channels at a time (refer to, e.g., NPL 3). As an element essential for such a communication system, development of an optical wavelength filter element serving as a wavelength separation element is currently underway (refer to, e.g., NPL 4).
In the development of a small-sized/sophisticated electronic apparatus typified by a recent mobile phone, a method of designing the electronic apparatus or method of testing the operation thereof becomes a major development item. This is because of that various kinds of electronic devices mounted inside the electronic apparatus at high density operate at high speed, so that malfunction of the devices may occur due to electromagnetic interference inside the apparatus. As the method of the device operation test that has frequently be used, a voltage wavelength measurement using a voltage probe having at its leading end a metal probe can be taken. This method can perform wavelength measurement only by bringing the metal probe into contact with a measurement point (metal portion) in principle, so that it is possible to easily determine the operating state of the device at short times.